1. Field of the Invention
The present invention relates to a circuit-forming charging powder and a multilayer wiring board using the same, especially to a circuit-forming charging powder (toner) to be used in printing a circuit pattern on an object by electrophotography, and a multilayer wiring board using the same.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 4-236484 discloses a method for forming a desired circuit pattern on an insulating substrate by taking advantage of the electrostatic force used in conventional electrophotography, and a circuit-forming charging powder to be used in this wiring method. FIG. 1 shows a cross section of the conventional circuit-forming charging powder. The circuit-forming charging powder 100 with a mean particle size of 10 to 15 xcexcm assumes a structure in which a conductive metal powder 101 and a charge control agent 102 are uniformly dispersed in a heat-melt resin 103. The practical method for producing the circuit-forming charging powder 100 comprises the steps of: mixing a flake-shaped silver powder with a mean particle size of 0.4 xcexcm as a conductive metal powder 101, a metallic azo dye as a charge control agent 102 and a styrene-acrylic acid copolymer as a heat-melt resin 103 in a weight ratio of 80:1:19, respectively; and heat-melting the mixture followed by kneading with a kneader. Then, the mixture is roughly crushed with a cutter mill, finely crushed with a jet mill and classified with an air jet, thereby obtaining the circuit-forming charging powder 100.
However, the conventional circuit-forming charging powder involves a problem in that the circuit pattern can peel off the baked ceramic sheet when the powder is used for printing the circuit pattern on a ceramic green sheet by electrophotography because the ceramic green sheet shrinks during baking.
Accordingly, the object of the present invention, carried out for solving the problem described above, provides a circuit-forming charging powder having little possibility for allowing the circuit pattern to be peeled off the printing object even when the circuit pattern is printed on the printing object by electrophotography, and a multilayer circuit board using the same.
According to the present invention, the circuit-forming charging powder to be used for printing a circuit pattern on a printing object by electrophotography comprises a conductive metal powder, a heat-melt resin, a charge control agent and an adhesion reinforcing agent.
The conductive metal powder is a secondary powder comprising aggregates formed by aggregating a plurality of primary powders, and the printing object is a ceramic green sheet.
The multilayer wiring board according to the present invention is formed by laminating and baking the ceramic green sheets on which the circuit pattern is printed.
The circuit-forming charging powder according to the present invention contains the adhesion reinforcing agent, which serves for allowing the conductive metal powder used for forming the circuit pattern to adhere with the baked ceramic sheet when the ceramic green sheet on which the circuit pattern has been printed is baked. Accordingly, the adhesion strength between the baked ceramic sheet and the circuit pattern is improved after baking, preventing the circuit pattern from being peeled off the ceramic sheet.
Also, the conductive metal powder constituting the circuit-forming charging powder is a secondary powder comprising an aggregate prepared by aggregating a plurality of primary powders, the conductive metal powder comprising the secondary powder being dissociated into primary powders when the circuit-forming charging powder is fixed. Accordingly, the circuit pattern formed with the primary powders constituting the conductive metal powder is densely packed, allowing the sheet resistance of the circuit pattern to be further reduced along with decreasing the circuit pattern loss.
Also, the adhesion reinforcing agent contained in the circuit-forming charging powder serves to allow the conductive metal powder to be formed into the circuit pattern and adhered with the baked ceramic sheet when the ceramic sheet on which the circuit pattern has been printed. Consequently, the adhesion strength of the baked ceramic sheet with the circuit pattern is improved after baking, prevent the circuit pattern from being peeled off the ceramic sheet.
Also, the multilayer wiring board according to the present invention is produced by the steps comprising: printing the circuit pattern on the ceramic green sheet by the electrophotographic method using the circuit-forming charging powder containing the adhesion reinforcing agent; and laminating the ceramic green sheets followed by baking. Accordingly, the circuit pattern has essentially no possibility to be peeled off the baked ceramic sheet after baking, making it possible to improve quality and reliability of the multilayer wiring board that can be used in high frequency bands.
Also, the multilayer wiring board is produced by the steps comprising: preparing the circuit-forming charging powder containing the conductive metal powder comprising the secondary powder of aggregates of a plurality of primary powders; and laminating the ceramic green sheet, on which the circuit pattern is printed by the electrophotographic method using the circuit-forming charging powder, followed by baking. Therefore, ceramic sheet resistance and loss of the circuit pattern is reduced along while making it possible to use the multilayer wiring board in higher frequency bands.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.